This invention concerns a process for preparing fibers of synthetic thermoplastic resin and, more particularly, to a process for preparing relatively short fibers of such thermoplastic resins as ethylene homopolymer, ethylene-vinyl acetate (EVA) copolymer and partially hydrolyzed ethylene-vinyl acetate (HEVA) terpolymer. Fibers resulting from the process of this invention have a variety of important industrial uses, e.g., as reinforcements for paper, non-woven fabrics and other web materials.
A number of processes are known for manufacturing fine powders of thermoplastic resin wherein the selected resin is dispersed in water containing a suitable resin dispersion-forming additive, e.g., a surface active agent or soap, at a temperature at or above the melting point of the polymer. Under the influence of vigorous agitation and aided by the dispersion-forming additive, the molten thermoplastic resin breaks up into minute particles of generally spheroidal shape, typically having an average particle diameter within the range of from about 20 to about 500 microns. Following cooling of the dispersion medium below the melting point of the resin the latter solidifies and is recovered as a fine powder, the individual particles for the most part preserving the spheroidal configuration which they possessed in the molten state. Processes of this type are described in, among others, U.S. Pat. Nos. 4,148,766; 4,148,768; 4,150,003; 4,151,003; 4,151,133 and 4,212,966. Of the foregoing, the processes of U.S. Pat. Nos. 4,150,003 and 4,151,133 employ an aqueous resin dispersion-forming medium containing an alkali metal soap of a higher carboxylic acid while the processes of U.S. Pat. Nos. 4,148,766 and 4,148,768, in addition to employing an alkali metal soap of a higher carboxylic acid, also employ a water-soluble salt to influence the particle size distribution of the displaced resin toward the lower end of the previously stated particle size range. U.S. Pat. No. 4,208,528 describes an aqueous resin dispersion-forming medium containing an alkali metal salt of an organophosphate ester and, optionally, a base such as sodium hydroxide to regulate particle size distribution. In all cases, the teachings of these prior art processes lead to the formation of resin particles of almost exclusively spheroidal configuration.